Accumulated evidence indicates that calcium homeostasis and intracellular calcium levels are altered during hormone action. Increases in cytoplasmic calcium may play a fundamental role in the "messenger" system of insulin, alpha-adrenergic agonists, and other hormones. Calmodulin is regarded as the primal "intracellular receptor" for calcium. This protein binds to a number of enzymes and proteins, conferring sensitivity to change in calcium concentration. Little is known of calmodulin function in hormonal intracellular messenger systems. Preliminary studies in our laboratory have revealed the existence of calmodulin-activated protein kinase in adipocyte microsomes (endoplasmic reticulum). The knowledge that protein kinases often function in hormonal intracellular messenger systems, and the ability of insulin to increase microsomal calcium uptake, makes further investigation of the kinase and its expression of great interest. This research plan proposes to study the problem with two approaches: 1. A cell-biological study of the effects of hormones on protein kinase activity. Adipocytes will be incubated with a wide range of hormones, conditions, and agents thought to effect calcium homeostasis. Changes in phosphorylation due to incubation with hormones will be measured. 2. An enzymological study of the microsomal calmodulin-dependent protein kinase and protein substrates. Studies will focus on comparison of the adipocyte enzyme to similar activities from other tissues, characterization of the microsomal kinase, and identification of the protein substrate of the kinase. If fully successful, this work will identify a hormone-modulated activity, regulated by a unique calmodulin-activated protein kinase. Demonstration of this regulatory mechanism will provide significant new evidence of a role for calmodulin as the intracellular calcium receptor in hormone action, and of regulation of an intracellular process by hormonal effects on calcium homeostasis.